The Lantian Formation is a 150-meter-thick sequence of rocks deposited in southern China during a 90-million-year epoch in the

Ediacaran The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and t ...

period. Its algal

macrofossil Macrofossils, also known as megafossils, are preserved organic remains large enough to be visible without a microscope. The term ''macrofossil'' stands in opposition to the term microfossil. Microfossils, by contrast, require substantial magnific ...

s (which have alternatively been interpreted as putative metazoans) are the oldest large and complex fossils known.

Sedimentology

The rocks were deposited in shallow seas, in the

photic zone The photic zone, euphotic zone, epipelagic zone, or sunlight zone is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological pro ...

yet below storm wave base, yet were deposited in predominantly anoxic conditions. The fossils are located on the bedding planes, and are randomly oriented. The lowest part of the formation consists of a cap dolomite, marking the end of the

Marinoan glaciation The Marinoan glaciation, sometimes also known as the Varanger glaciation, was a period of worldwide glaciation that lasted from approximately 650 to 632.3 ± 5.9 Ma (million years ago) during the Cryogenian period. This glaciation possibly cov ...

and start of the Ediacaran. Above this is black shale containing the Lantian biota fossils. Above this are layers of dolomite, and shale followed by limestone. The highest part of the formation is black shale again. Above the formation is the Piyuancun formation consisting of silicious rock. The Lantian formation overlies

diamictite Diamictite (; from Ancient Greek ''δια'' (dia-): ''through'' and ''µεικτός'' (meiktós): ''mixed'') is a type of lithified sedimentary rock that consists of nonsorted to poorly sorted terrigenous sediment containing particles that r ...

from the Cryogenian.supplementary figure 4 of

Taphonomy

The fossils are preserved as carbonaceous films in a

Burgess Shale type preservation The Burgess Shale of British Columbia is famous for its exceptional preservation of mid-Cambrian organisms. Around 69 other sites have been discovered of a similar age, with soft tissues preserved in a similar, though not identical, fashion. Additi ...

al fashion. '' Anhuiphyton lineatum'' is one example of a fossil located in the site.

Age

Originally presumed to be Cambrian in age, the formation is now correlated with the

Doushantuo formation The Doushantuo Formation (formerly transcribed as Toushantuo or Toushantou, from ) is a geological formation in western Hubei, eastern Guizhou, southern Shaanxi, central Jiangxi, and other localities in China. It is known for the fossil Lagers ...

, with an overlying formation also falling in the Ediacaran period. The Lantian biota has a maximum Re-Os age of .

References

{{reflist Ediacaran Asia Ediacaran life Ediacaran geology Proterozoic Eonothem of Asia